(Paul Michael Brown) wrote in
news
The only gear I never really understood was the APX-6
transponder. I always kept a wary eye on that live round .45 shell
aimed at the Top Secret cavitron.

This cries out for further explanation. From context, I assume the
idea was to prevent the bad guys from reverse engineering the IFF and
figuring out a method to interrogate it. But was the self destruct
mechanism *really* a live .45 calibre shell?

I don't think so, but there was a CAD in each of the three cavities to
destroy them, The idea was to keep the bad guys from determining the
operating frequency, which, at that time, was changed every day. Later
on, after an intact unit was compromised, the SIF coder was added to the
system and the frequencies were fixed at 1030 and 1090 MHz. Mode 4 came
much later.